The present invention relates to apparatus and method for chemical/mechanical polishing for planarizing the surface of a film, such as a conductor film or an insulator film, deposited on a semiconductor substrate in multilevel interconnect and/or element isolation processes of a semiconductor integrated circuit.
Chemical/mechanical polishing (CMP) enables global planarization of a substrate, which cannot be accomplished by any other planarization technique such as resist etch-back. Thus, CMP is one of most noticeable planarization techniques suitably employed for fabricating a semiconductor integrated circuit being miniaturized day by day. In addition, by performing CMP, various problems, such as inaccurate exposure resulting from the variation in depths of focus during a lithography process and inferior reliability of wires formed on a non-planarized surface, can be solved.
A conventional chemical/mechanical polishing apparatus (hereinafter, simply referred to as a "CMP polisher") will be described with reference to FIG. 10. FIG. 10 is a schematic representation illustrating an arrangement for a conventional CMP polisher.
As shown in FIG. 10, a substrate 1 to be polished, made of silicon or the like, is held by a substrate holder 2, which is rotatable and vertically movable. A polishing pad 3 for polishing the surface of the substrate 1 is attached to the planar surface of a polishing platen 4 for moving rotationally. An abrasive (in a slurry state) 5 is supplied through an abrasive supply tube 6 every time by a predetermined amount and dripped onto the polishing pad 3.
In the CMP polisher having such an arrangement, when the polishing platen 4 is rotated with the abrasive 5 dripped through the abrasive supply tube 6 onto the polishing pad 3, the polishing pad 3 is also rotated correspondingly. And when the substrate holder 2 is brought down while rotating, then the substrate 1, held by the substrate holder 2, comes into contact with the polishing pad 3. As a result, the surface of the substrate 1 is polished. The CMP polisher shown in FIG. 10 includes a single substrate holder 2. Accordingly, the polisher is of the type polishing a single substrate 1 during a single polishing process step. Alternatively, if a CMP polisher having a plurality of substrate holders 2 is used, then a plurality of substrates 1 can be polished in parallel with each other during a single polishing process step.
However, if polishing is performed by getting a large number of substrates 1 into contact with the polishing pad 3 one after another, then the polishing surface of the polishing pad 3 gradually loses its capacity to hold the abrasive 5. This is because as polishing is performed for a longer and longer time, the polishing surface of the polishing pad 3 gets more and more clogged owing to the deposition of polishing debris, the mass of abrasive particles and the like. As a result, the amount of the abrasive 5, held in a polishing region where the polishing pad 3 and the substrate 1 are in contact with each other, decreases, and consequently the number of abrasive particles contained in the abrasive 5 also decreases. Accordingly, a rate at which the substrate 1 is polished (hereinafter, simply referred to as a "polishing rate") adversely decreases.
Thus, it is necessary to re-increase and stabilize the polishing rate by rejuvenating the clogged polishing pad 3 through dressing. "Dressing" is a process step for recovering the polishing pad's 3 capacity to hold the abrasive 5 by eliminating clogging from the polishing pad 3. Clogging can be eliminated, for example, by rotating and pressing a dresser 7, to which fine particles of diamond or the like are embedded, against the polishing pad 3. If dressing is performed at regular intervals, then the polishing rate for a substrate can be increased and the variation in polishing rates among substrates can be reduced.
In general, the dressing process step is performed every time a number of substrates have been polished over a predetermined amount of time or every time the number of substrates polished has reached a predetermined number. Also, the dressing process step is performed either in parallel with the polishing process step of a substrate or in an interval between the polishing process steps of substrates.
The amount and number of abrasive particles, which exist on a polishing pad and contributing to polishing, are variable depending upon the roughness of the polishing surface of the polishing pad. Accordingly, the polishing rate of a substrate is also considerably affected by the variation in roughness of the polishing surface of the polishing pad. Thus, in order to keep a polishing rate constant, the roughness of the polishing surface of the polishing pad is desirably kept constant.
However, no method has heretofore been suggested for sensing the roughness of the polishing surface of a polishing pad. Accordingly, as described above, dressing is performed every time a number of substrates have been polished over a predetermined amount of time or every time the number of substrates polished has reached a predetermined number.
Since the roughness of the polishing surface of a polishing pad cannot be kept constant, various inconveniences are very likely to occur in the case of sequentially polishing a large number of substrates. For instance, the polishing rates are gradually decreased or varied among the substrates because the polishing pad gets clogged. Also, since the surface of the polishing pad is glazed, trouble tends to happen in transporting a substrate being held on a substrate holder. Specifically, it becomes less easy to take away the substrate from the polishing pad.